Method for manufacturing optical device, and optical device wafer

ABSTRACT

A method for manufacturing an optical device includes the steps of: forming a first multilayer film, including forming a first mirror above a substrate, forming an active layer above the first mirror, forming a second mirror above the active layer, forming a semiconductor layer on the second mirror, and forming a sacrificial layer on the semiconductor layer; conducting a first examination step of conducting a reflectance examination on the first multilayer film; forming a second multilayer film by removing the sacrificial layer from the first multilayer film; conducting a second examination step of conducting a reflection coefficient examination on the second multilayer film; and patterning the second multilayer film to form a surface-emitting laser section having the first mirror, the active layer and the second mirror, and a diode section having the semiconductor layer, wherein the sacrificial layer is formed to have an optical film thickness of an odd multiple of λ/4, where λ is a design wavelength of light emitted by the surface-emitting laser section.

The entire disclosure of Japanese Patent Application Nos: 2006-194,filed Jul. 14, 2006 and 2007-106844, filed Apr. 16, 2007 are expresslyincorporated by reference herein.

BACKGROUND

1. Technical Field

Several aspects of the present invention relate to methods formanufacturing optical devices, and optical device wafers.

2. Related Art

A surface-emitting type semiconductor laser has a characteristic inwhich its optical output changes depending on the ambient temperature.For this reason, an optical module that uses a surface-emitting typesemiconductor laser may be equipped with a photodetecting function fordetecting a portion of a laser beam emitted from the surface-emittingtype semiconductor laser to monitor its optical output value. Forexample, a photodetector device such as a photodiode may be provided ona surface-emitting type semiconductor laser, whereby a portion of alaser beam emitted from the surface-emitting type semiconductor lasercan be monitored within the same device. For example, Japanese laid-openpatent application JP-A-10-135568 is an example of related art.

SUMMARY

In accordance with an advantage of some aspects of the invention, thereis provided a method for manufacturing an optical device including asurface-emitting laser section and a diode section and having desiredcharacteristics. Also, an optical device wafer that is used in theaforementioned method for manufacturing an optical device is provided.

In accordance with an embodiment of the invention, a first method formanufacturing an optical device includes the steps of:

forming a first multilayer film, including forming a first mirror abovea substrate, forming an active layer above the first mirror, forming asecond mirror above the active layer, forming a semiconductor layer onthe second mirror, and forming a sacrificial layer on the semiconductorlayer;

conducting a first examination step of conducting a reflectanceexamination on the first multilayer film;

forming a second multilayer film by removing the sacrificial layer fromthe first multilayer film;

conducting a second examination step of conducting a reflectanceexamination on the second multilayer film; and

patterning the second multilayer film to form a surface-emitting lasersection having the first mirror, the active layer and the second mirror,and a diode section having the semiconductor layer,

wherein an optical film thickness of the sacrificial layer is formed tobe an odd multiple of λ/4, where λ is a design wavelength of lightemitted by the surface-emitting laser section.

According to the method for manufacturing an optical device, areflectance profile of the first multilayer film is obtained by thefirst examination step, and a reflectance profile of the secondmultilayer film is obtained by the second examination step, such thatthe multilayer film obtained by forming layers above the substrate canbe accurately evaluated. By this, manufacture of an optical device witha defective multilayer film can be avoided beforehand. Accordingly, bythe method for manufacturing an optical device, optical devices havingdesired characteristics can be securely provided.

It is noted that, in descriptions concerning the invention, the term“above” may be used, for example, in a manner as “a specific member(hereafter referred to as ‘B’) formed ‘above’ another specific member(hereafter referred to as ‘A’).” In descriptions concerning theinvention, the term “above” is used, in such an exemplary case describedabove, assuming that the use of the term includes a case in which “B” isformed directly on “A,” and a case in which “B” is formed over “A”through another member on “A.”

Also, in the present invention, the “design wavelength” is a wavelengthof light that is expected, at a designing stage in designing an opticaldevice, to have the maximum intensity among light emitted from thesurface-emitting laser.

Also, in the present invention, the “optical film thickness” is a valueobtained by multiplying an actual film thickness of a layer and arefractive index of material composing the layer.

In the method for manufacturing an optical device in accordance with anaspect of the embodiment of the invention, an optical film thickness ofthe semiconductor layer may be formed to be an odd multiple or an evenmultiple of λ/4.

It is noted that, in the present invention, the case of being an oddmultiple of λ/4 may include a case of perfectly matching with an oddmultiple of λ/4 and a case of generally matching with an odd multiple ofλ/4. Similarly, in the present invention, the case of being an evenmultiple of λ/4 may include a case of perfectly matching with an evenmultiple of λ/4 and a case of generally matching with an even multipleof λ/4.

In the method for manufacturing an optical device in accordance with anaspect of the embodiment of the invention, an optical film thickness ofthe semiconductor layer may be formed to be an odd multiple of λ/4, areflection band of the first mirror and the second mirror may bemeasured in the first examination step, and a Fabry-Perot wavelength oflight emitted by the surface-emitting laser section may be measured inthe second examination step.

It is noted that, in the present invention, the “Fabry-Perot wavelengthof light that is emitted by the surface-emitting laser section” is awavelength of light having the maximum intensity among light that isactually emitted by the surface-emitting laser section.

In the method for manufacturing an optical device in accordance with anaspect of the embodiment of the invention, an optical film thickness ofthe semiconductor layer may be formed to be an even multiple of λ/4, aFabry-Perot wavelength of light emitted by the surface-emitting lasersection may be measured in the first examination step, and a reflectionband of the first mirror and the second mirror may be measured in thesecond examination step.

In the method for manufacturing an optical device in accordance with anaspect of the embodiment of the invention, in the step of removing thesacrificial layer, a layer among the semiconductor layer in contact withthe sacrificial layer may function as an etching stopper layer.

In the method for manufacturing an optical device in accordance with anaspect of the embodiment of the invention, the sacrificial layer may beformed from InGaP, and the layer among the semiconductor layer incontact with the sacrificial layer may be formed from AlGaAs or GaAs.

In the method for manufacturing an optical device in accordance with anaspect of the embodiment of the invention, the sacrificial layer may beformed from AlGaAs, and the layer among the semiconductor layer incontact with the sacrificial layer may be formed from GaAs.

In the method for manufacturing an optical device in accordance with anaspect of the embodiment of the invention, the diode section may beformed to be a photodetector section, and the semiconductor layer may beformed to include a photoabsorption layer.

It is noted that, in the present invention, the “photoabsorption layer”conceptually includes a depletion layer.

In the method for manufacturing an optical device in accordance with anaspect of the embodiment of the invention, the semiconductor layer mayinclude a first contact layer of a first conductivity type, and a secondcontact layer of a second conductivity type formed above the firstcontact layer.

In the method for manufacturing an optical device in accordance with anaspect of the embodiment of the invention, the first mirror and thesecond mirror may be formed from distributed Bragg reflection typemirrors, and an optical film thickness of each layer in the distributedBragg reflection type mirrors may be λ/4.

In accordance with an embodiment of the invention, a second method formanufacturing an optical device includes the steps of:

forming a first multilayer film, including forming a first mirror abovea substrate, forming an active layer above the first mirror, forming asecond mirror above the active layer, forming a semiconductor layer onthe second mirror, and forming a sacrificial layer on the semiconductorlayer;

conducting a first examination step of conducting a reflectanceexamination on the first multilayer film;

forming a second multilayer film by removing the sacrificial layer fromthe first multilayer film;

conducting a second examination step of conducting a reflectanceexamination on the second multilayer film; and

patterning the second multilayer film to form a surface-emitting lasersection having the first mirror, the active layer and the second mirror,and a diode section having the semiconductor layer,

wherein, in the first examination step, a first measurement of measuringa reflection band of the first mirror and the second mirror or a secondmeasurement of measuring a Fabry-Perot wavelength of light emitted bythe surface-emitting laser section is conducted; and

in the second examination step, the second measurement is conducted whenthe first measurement is conducted in the first examination step, andthe first measurement is conducted when the second measurement isconducted in the first examination step.

In accordance with still another embodiment of the invention, an opticaldevice wafer includes:

a substrate;

a first mirror formed above the substrate;

an active layer formed above the first mirror;

a second mirror formed above the active layer;

a semiconductor layer formed on the second mirror; and

a sacrificial layer formed on the semiconductor layer,

wherein the first mirror, the active layer and the second mirror areused to form at least a portion of a surface-emitting laser section,

the semiconductor layer is used to form at least a portion of a diodesection, and

an optical film thickness of the sacrificial layer is an odd multiple ofλ/4, where λ is a design wavelength of light that is emitted by thesurface-emitting laser section.

In the optical device wafer in accordance with an aspect of theembodiment of the invention, an optical film thickness of thesemiconductor layer may be an odd multiple or an even multiple of λ/4.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of an optical device inaccordance with an embodiment of the invention.

FIG. 2 is a schematic cross-sectional view of the optical device inaccordance with the embodiment.

FIG. 3 is a schematic plan view of the optical device in accordance withthe embodiment.

FIG. 4 is a cross-sectional view schematically showing a step in amethod for manufacturing an optical device in accordance with anembodiment of the invention.

FIG. 5 is a graph schematically showing a reflectance profile of amultilayer film in accordance with an embodiment of the invention.

FIG. 6 is a graph schematically showing a reflectance profile of amultilayer film in accordance with an embodiment of the invention.

FIG. 7 is a cross-sectional view schematically showing a step in amethod for manufacturing an optical device in accordance with anembodiment of the invention.

FIG. 8 is a cross-sectional view schematically showing a step in themethod for manufacturing an optical device in accordance with theembodiment.

FIG. 9 is a graph showing the relation between the optical filmthickness of a pin section and the output of an optical device.

FIG. 10 is a cross-sectional view schematically showing a first modifiedexample of the optical device in accordance with the present embodiment.

FIG. 11 is a diagram showing a third modified example of the opticaldevice in accordance with the present embodiment.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Preferred embodiments of the invention are described below withreference to the accompanying drawings.

1. First, an optical device 100 in accordance with an embodiment of theinvention is described.

FIG. 1 and FIG. 2 are schematic cross-sectional views of the opticaldevice 100, and FIG. 3 is a schematic plan view of the optical device100. It is noted that FIG. 1 is a cross-sectional view taken along aline I-I of FIG. 3, and FIG. 2 is a cross-sectional view taken along aline II-II of FIG. 3.

The optical device 100 in accordance with the present embodiment mayinclude, as shown in FIG. 1 through FIG. 3, a substrate 101, asurface-emitting laser section 140, a diode section 120, first-fourthelectrodes 107, 109, 116 and 110, and first-third dielectric layers 30,32 and 40.

As the substrate 101, for example, a GaAs substrate of a firstconductivity type (for example, n-type) may be used.

The surface-emitting laser section 140 is formed on the substrate 101.The surface-emitting laser section 140 includes a first mirror 102 ofthe first conductivity type (n-type), an active layer 103 formed on thefirst mirror 102, and a second mirror 104 of a second conductivity type(for example, p-type) formed on the active layer 103. More concretely,the first mirror 102 is, for example, a distributed Bragg reflectiontype (DBR) mirror of 40.5 pairs of alternately laminated n-typeAl_(0.9)Ga_(0.1)As layers and n-type Al_(0.12)Ga_(0.88)As layers. Theactive layer 103 has a multiple quantum well (MQW) structure in whichquantum well structures each formed from, for example, a GaAs well layerand an Al_(0.3)Ga_(0.7)As barrier layer are laminated in three layers.The second mirror 104 includes, for example, a DBR mirror of 23 pairs ofalternately laminated p-type Al_(0.9)Ga_(0.1)As layers and p-typeAl_(0.12)Ga_(0.88)As layers, and a p-type GaAs layer (the topmost layerof the second mirror 104) 14 formed thereon. Each layer in the DBRmirrors has an optical film thickness of λ/4. It is noted that λ is adesign wavelength of light that is emitted by the surface-emitting lasersection 140. It is noted that the composition of each of the layers andthe number of the layers composing the first mirror 102, the activelayer 103 and the second mirror 104 are not particularly limited to theabove.

The first mirror 102, the active layer 103 and the second mirror 104 canform a vertical resonator. The p-type second mirror 104, the activelayer 103 that is not doped with an impurity and the n-type first mirror102 form a pin diode. A portion of the first mirror 102, the activelayer 103 and the second mirror 104 may form, for example, a columnarsemiconductor laminate (hereafter referred to as a “columnar section”)130. The columnar section 130 has a plane configuration that is, forexample, in a circular shape.

Also, as shown in FIG. 1 and FIG. 2, for example, at least one of thelayers composing the second mirror 104 can be formed as a currentconstricting layer 105. The current constricting layer 105 is formed ina region near the active layer 103. As the current constricting layer105, for example, an oxidized AlGaAs layer can be used. The currentconstricting layer 105 is a dielectric layer having an opening section,and is formed in a ring shape.

The first electrode 107 is formed on a top surface of the first mirror102. The first electrode 107 is electrically connected to the firstmirror 102. The first electrode 107 may include a contact section 107 a,a lead-out section 107 b and a pad section 107 c, as shown in FIG. 3.The first electrode 107 is in contact with the first mirror 102 at thecontact section 107 a. The lead-out section 107 b of the first electrode107 connects the contact section 107 a with the pad section 107 c. Thepad section 107 c of the first electrode 107 is connected as anelectrode pad to an external wiring or the like. The first electrode 107may be formed from a multilayer film in which, for example, layers of analloy of gold (Au) and germanium (Ge), and gold (Au) are laminated inthis order. It is noted that, in the illustrated example, the firstelectrode 107 is provided on the first mirror 102. However, the firstelectrode 107 may be provided at a back surface 101 b of the substrate101.

The second electrode 109 is formed on the second mirror 104 and thefirst dielectric layer 30. The second electrode 109 is electricallyconnected to the second mirror 104. The second electrode 109 may includea contact section 109 a, a lead-out section 109 b and a pad section 109c, as shown in FIG. 3. The second electrode 109 is in contact with thesecond mirror 104 at the contact section 109 a. The lead-out section 109b of the second electrode 109 connects the contact section 109 a withthe pad section 109 c. The pad section 109 c of the second electrode 109is connected as an electrode pad to an external wiring or the like. Thesecond electrode 109 may be formed from a multilayer film in which, forexample, layers of platinum (Pt), titanium (Ti) and gold (Au) arelaminated in this order.

The first dielectric layer 30 is formed on the first mirror 102. Thefirst dielectric layer 30 is formed in a manner to surround the columnarsection 130. The lead-out section 109 b and the pad section 109 c of thesecond electrode 109 are formed on the first dielectric layer 30. Thefirst dielectric layer 30 can electrically isolate the second electrode109 from the first mirror 102. For example, as the first dielectriclayer 30, a resin layer composed of polyimide resin or the like can beused.

The second dielectric layer 32 is formed on the second mirror 104 andthe first dielectric layer 30. The second dielectric layer 32 is formedin contact with a portion of the side surface of the columnar sectioncomposed of the isolation layer 20 and the first contact layer 111. Alead-out section 116 b and a pad section 116 c of the third electrode116 are formed on the second dielectric layer 32. The second dielectriclayer 32 can electrically isolate the third electrode 116 from thesecond mirror 104. For example, as the second dielectric layer 32, aninorganic dielectric layer composed of silicon oxide or the like can beused.

The diode section 120 is formed on the surface-emitting laser section140. The diode section 120 can function, for example, as a photodetectorsection. The diode section 120 can monitor, for example, an output oflight generated by the surface-emitting laser 140. The diode section 120includes a semiconductor layer 122. The semiconductor layer 122 may beformed from, for example, a plurality of semiconductor layers. Thesemiconductor layer 122 may include, for example, an isolation layer 20,a first contact layer 111 formed on the isolation layer 20, aphotoabsorption layer 112 formed on the first contact layer 111, and asecond contact layer 113 formed on the photoabsorption layer 112.

The isolation layer 20 may be composed of AlGaAs of intrinsicsemiconductor. The isolation layer 20 and the first contact layer 111may compose, for example, a columnar semiconductor laminate (columnarsection). The columnar section has a plane configuration that is, forexample, a circular shape. The first contact layer 111 may be composedof, for example, an n-type GaAs layer. The photoabsorption layer 112 maybe composed of, for example, a GaAs layer in which no impurity is doped.The second contact layer 113 may be composed of, for example, a p-typeGaAs layer. An energy gap of the constituent material of at least onelayer of the layers composing the semiconductor layer 122 is narrowerthan, for example, an energy gap of the constituent material of thefirst mirror 102 and the second mirror 104 of the surface-emitting lasersection 140.

The p-type second contact layer 113, the photoabsorption layer 112 inwhich no impurity is doped, and the n-type first contact layer 111 forma pin diode. The second contact layer 113 and the photoabsorption layer112 may form, for example, a columnar semiconductor laminate (columnarsection). The columnar section has a plane configuration that is, forexample, a circular shape.

The third electrode 116 is formed on the first contact layer 111 and thesecond dielectric layer 32. The third electrode 116 is electricallyconnected to the first contact layer 111. The third electrode 116 mayinclude a contact section 116 a, a lead-out section 116 b and a padsection 116 c, as shown in FIG. 3. The third electrode 116 is in contactwith the first contact layer 111 at the contact section 116 a. Thelead-out section 116 b of the third electrode 116 connects the contactsection 116 a with the pad section 116 c. The pad section 116 c of thethird electrode 116 is connected as an electrode pad to an externalwiring or the like. The third electrode 116 may be composed of the samematerial as that of, for example, the first electrode 107.

The fourth electrode 110 is formed on the second contact layer 113 andthe third dielectric layer 40. The fourth electrode 110 is electricallyconnected to the second contact layer 113. The fourth electrode 110 mayinclude a contact section 110 a, a lead-out section 110 b and a padsection 110 c, as shown in FIG. 3. The fourth electrode 110 is incontact with the second contact layer 113 at the contact section 110 a.The contact section 110 a has an opening section on the second contactlayer 113. The opening section forms an area where the contact section110 a is not formed on the top surface of the second contact layer 113.This area defines, for example, a laser emission surface 108. Thelead-out section 110 b of the fourth electrode 110 connects the contactsection 110 a with the pad section 110 c. The pad section 110 c of thefourth electrode 110 is connected as an electrode pad to an externalwiring or the like. The fourth electrode 110 may be composed of the samematerial as that of, for example, the second electrode 109.

The third dielectric layer 40 is formed on the first contact layer 111and the second dielectric layer 32. The third dielectric layer 40 isformed in a manner to surround the columnar section that is composed ofthe photoabsorption layer 112 and the second contact layer 113. Thelead-out section 110 b and the pad section 110 c of the fourth electrode110 are formed on the third dielectric layer 40. The third dielectriclayer 40 can electrically isolate the fourth electrode 110 from thefirst contact layer 111. As the third dielectric layer 40, an inorganicdielectric layer composed of, for example, silicon oxide of the like canbe used.

2. Next, an example of a method for manufacturing the optical device 100in accordance with an embodiment of the invention is described withreference to the accompanying drawings.

FIG. 4, FIG. 7 and FIG. 8 are cross-sectional views schematicallyshowing a process for manufacturing the optical device 100 of thepresent embodiment shown in FIGS. 1-3, and correspond to thecross-sectional view shown in FIG. 1, respectively.

(1) First, as shown in FIG. 4, for example, an n-type GaAs substrate isprepared as a substrate 101. Then, a first semiconductor multilayer film150 is formed on the substrate 101 by epitaxial growth while modifyingits composition, whereby an optical device wafer 200 is obtained.Concretely, the optical device wafer 200 is obtained in the followingmanner.

First, semiconductor layers that compose a first mirror 102, an activelayer 103 and a second mirror 104 are laminated on the substrate 101.When the second mirror 104 is grown, at least one layer thereof near theactive layer 103 is formed to be a layer that is later oxidized andbecomes a current constricting layer 105. As the layer to be oxidized,for example, an AlGaAs layer with its Al composition being 0.95 orhigher may be used.

Then, a semiconductor layer 122 (more specifically, an isolation layer20, a first contact layer 111, a photoabsorption layer 112 and a secondcontact layer 113) may be formed directly on the second mirror 104. Thesemiconductor layer 122 is formed to have an optical film thickness thatis an odd multiple or an even multiple of λ/4. It is noted that λ is adesign wavelength of light that is emitted by the surface-emitting lasersection 140.

For example, when the optical film thickness of the semiconductor layer122 is set to be an odd multiple of λ/4, the optical film thickness ofthe isolation layer 20 may be set to an even multiple of λ/4, and thetotal optical film thickness of the first contact layer 111, thephotoabsorption layer 112 and the second contact layer 113 (hereafteralso referred to as the “pin section”) may be set to an odd multiple ofλ/4. Alternatively, for example, the optical film thickness of theisolation layer 20 may be set to an odd multiple of λ/4, and the opticalfilm thickness of the pin section may be set to an even multiple of λ/4.

Also, for example, when the optical film thickness of the semiconductorlayer 122 is set to be an even multiple of λ/4, for example, the opticalfilm thickness of the isolation layer 20 may be set to an odd multipleof λ/4, and the optical film thickness of the pin section may be set toan odd multiple of λ/4. Alternatively, for example, the optical filmthickness of the isolation layer 20 may be set to an even multiple ofλ/4, and the optical film thickness of the pin section may be set to aneven multiple of λ/4.

Then, a sacrificial layer 60 may be formed directly on the semiconductorlayer 122. The sacrificial layer 60 may be formed to have an opticalfilm thickness that is an odd multiple of λ/4. By this, for example,when the semiconductor layer 122 has an optical film thickness that isan odd multiple of λ/4, the total optical film thickness of thesemiconductor layer 122 and the sacrificial layer 60 would become aneven multiple of λ/4. Also, for example, when the semiconductor layer122 has an optical film thickness that is an even multiple of λ/4, thetotal optical film thickness of the semiconductor layer 122 and thesacrificial layer 60 would become an odd multiple of λ/4.

By the steps described above, the first multilayer film 150 can beformed, and thus the optical device wafer 200 can be obtained.

(2) Next, a reflectance examination (first examination step) isconducted on the first multilayer film 150. The reflectance examinationmay be conducted, for example, as shown in FIG. 4, through irradiatinglight 11 from a light source 10 that emits white light through adiffraction grating (not shown) on a surface of the first multilayerfilm 150, and making reflected light 13 incident upon a photodetectordevice 12 such as a CCD through a mirror (not shown).

In the first examination step, when the total optical film thickness ofthe semiconductor layer 122 and the sacrificial layer 60 is an evenmultiple of λ/4, a reflectance profile D that is shown, for example, inFIG. 5 can be obtained. It is noted that FIG. 5, and FIG. 6 (to bedescribe below) show a reflectance profile V of a multilayer filmcomposed of a first mirror 102, an active layer 103 and a second mirror104 formed on the substrate 101 (in other words, the multilayer filmwithout having the semiconductor layer 122) in a dot-and-dash line. Inaccordance with the present embodiment, for example, as indicated by thereflectance profile V, a region W between wavelengths λ₁ and λ₂ at whichthe reflectance becomes half of its maximum value can be set as areflection band of the DBR mirrors composing the first mirror 102 andthe second mirror 104. A dip is observed in the reflectance profile V ofthe multilayer film that does not have the semiconductor layer 122, asshown in FIG. 5. The wavelength at the lowest point of the dip is aFabry-Perot wavelength λ_(f) of light that is emitted from thesurface-emitting laser section 140.

It is noted that, for example, when the total optical film thickness ofthe semiconductor layer 122 and the sacrificial layer 60 is an evenmultiple of λ/4, a reflectance profile D of the first multilayer film150 shown in FIG. 5 is obtained. With the reflectance profile D,photoabsorption that is originated from the semiconductor layer 122occurs near the dip described above, such that measurement of aFabry-Perot wavelength λ_(f) becomes difficult. However, theabove-described reflection band W of the first mirror 102 and the secondmirror 104 can be accurately measured.

Also, in the first examination step, when the total optical filmthickness of the semiconductor layer 122 and the sacrificial layer 60 isan odd multiple of λ/4, a reflectance profile D that is shown, forexample, in FIG. 6 is obtained. With the reflectance profile D of thefirst multilayer film 150 in this case, photoabsorption that isoriginated from the semiconductor layer 122 occurs near both ends of thereflection band W of the DBR mirrors, as shown in FIG. 6, such thatmeasurement of the reflection band W of the DBR mirrors becomesdifficult. However, the Fabry-Perot wavelength λ_(f) indicated by theabove-described dip can be accurately measured.

(3) Next, as shown in FIG. 7, the sacrificial layer 60 is removed fromthe first multilayer film 150, thereby forming a second multilayer film152. The sacrificial layer 60 may be removed by, for example, a wetetching method. When the sacrificial layer 60 is removed, a layer thatis in contact with the sacrificial layer 60 among the semiconductorlayer 122 (e.g., the second contact layer 113 in the illustratedexample) can be functioned as an etching stopper layer. As the etchantused in this step, an etchant with which the etching stopper layer(e.g., the second contact layer 113) would be more difficult to beetched compared to the sacrificial layer 60 may be selected. In otherwords, an etchant with which the etching rate of the second contactlayer 113 is lower than the etching rate of the sacrificial layer 60 canbe selected. By this, when etching the sacrificial layer 60, the etchingcan be readily stopped at the time when the top surface of the secondcontact layer 113 is exposed. In the present embodiment, for example,the sacrificial layer 60 may be composed of InGaP, and the secondcontact layer 113 may be composed of AlGaAs or GaAs. In this case, amixed solution of phosphoric acid (H₃PO₄), hydrogen peroxide solution(H₂O₂) and water may be used as the etchant, whereby the etching rate ofthe second contact layer 113 can be made lower. Also, in the presentembodiment, for example, the sacrificial layer 60 may be composed ofAlGaAs, and the second contact layer 113 may be composed of GaAs. Inthis case, diluted hydrofluoric acid (HF+H₂O) or buffered hydrofluoricacid (NH₄F+H₂O) may be used as the etchant, whereby the etching rate ofthe second contact layer 113 can be made lower.

It is noted that, for example, the sacrificial layer 60 and the secondcontact layer 113 may be composed of the same material. In this case,when etching the sacrificial layer 60, for example, the etching time maybe controlled, whereby the etching can be stopped at the time when thetop surface of the second contact layer 113 is exposed.

(4) Next, a reflectance examination (second examination step) isconducted on the second multilayer film 152. The reflectance examinationmay be conducted in a manner similar to the first examination stepdescribed above, as shown in FIG. 7.

For example, when the total optical film thickness of the semiconductorlayer 122 and the sacrificial layer 60 is an even multiple of λ/4 in thefirst examination step, a reflectance profile D that is shown, forexample, in FIG. 6 is obtained because the optical film thickness of thesemiconductor layer 122 is an odd multiple of λ/4 in the secondexamination step. With the reflectance profile D of the secondmultilayer film 152 in this case, the Fabry-Perot wavelength λ_(f)indicated by the dip can be accurately measured, as shown in FIG. 6, ina similar manner described above with respect to the first examinationstep. Accordingly, in this case, as described above, the reflection bandW of the first mirror 102 and the second mirror 104 can be accuratelyobserved (first measurement) in the first examination step, and theFabry-Perot wavelength λ_(f) can be accurately measured (secondmeasurement) in the second examination step.

Further, for example, when the total optical film thickness of thesemiconductor layer 122 and the sacrificial layer 60 is an odd multipleof λ/4 in the first examination step, a reflectance profile D that isshown, for example, in FIG. 5 is obtained because the optical filmthickness of the semiconductor layer 122 is an even multiple of λ/4 inthe second examination step. With the reflectance profile D of thesecond multilayer film 152 in this case, the reflection band W of thefirst mirror 102 and the second mirror 104 can be accurately observed,as shown in FIG. 5, in a similar manner described above with respect tothe first examination step. Accordingly, in this case, as describedabove, the Fabry-Perot wavelength λ_(f) can be accurately measured(second measurement) in the first examination step, and the reflectionband W of the first mirror 102 and the second mirror 104 can beaccurately observed (first measurement) in the second examination step.

(5) Then, the second multilayer film 152 is patterned, thereby forming afirst mirror 102, an active layer 103, a second mirror 104, and asemiconductor layer 122 (including an isolation layer 20, a firstcontact layer 111, a photoabsorption layer 112 and a second contactlayer 113) each in a desired configuration, as shown in FIG. 8. By this,each of the columnar sections is formed. The second multilayer film 152may be patterned by using, for example, lithography technique andetching technique.

Then, by placing the substrate 101 on which the columnar sections areformed through the aforementioned steps in a water vapor atmosphere, forexample, at about 400° C., the layer to be oxidized described above isoxidized from its side surface, thereby forming the current constrictinglayer 105.

(6) Next, as shown in FIG. 1 through FIG. 3, a first dielectric layer 30is formed on the first mirror 102. First, a dielectric layer composed ofpolyimide resin or the like is formed over the entire surface by using,for example, a spin coat method. Then, the top surface of the columnarsection 130 is exposed by using, for example, an etch-back method. Then,the dielectric layer is patterned by, for example, lithography techniqueand etching technique. In this manner, the first dielectric layer 30 ina desired configuration can be formed.

Then, as shown in FIG. 1 through FIG. 3, a second dielectric layer 32 isformed on the second mirror 104 and the first dielectric layer 30.First, a dielectric layer composed of silicon oxide or the like isformed over the entire surface by using, for example, a plasma CVDmethod. Then, the dielectric layer is patterned by using, for example,lithography technique and etching technique. In this manner, the seconddielectric layer 32 in a desired configuration can be formed.

Then, as shown in FIG. 1 through FIG. 3, a third dielectric layer 40 isformed on the first contact layer 111 and the second dielectric layer32. The method for forming the third dielectric layer 40 may be the sameas, for example, the method for forming the second dielectric layer 32described above.

Then, first through fourth electrodes 107, 109, 116 and 110 are formed.The electrodes may be formed in desired configurations, respectively,by, for example, a combination of a vacuum vapor deposition method and alift-off method, or the like. The order of forming the electrodes is notparticularly limited.

(7) By the steps described above, the optical device 100 in accordancewith the present embodiment is formed, as shown in FIG. 1 through FIG.3.

3. In accordance with the present embodiment, as described above, areflectance profile of the first multilayer film 150 is obtained in thefirst examination step, and a reflectance profile of the secondmultilayer film 152 is obtained in the second examination step, suchthat the multilayer film obtained through forming layers above thesubstrate 101 can be accurately evaluated. By this, manufacturer of anoptical device with a defective multilayer film can be avoidedbeforehand. Accordingly, by the method for manufacturing an opticaldevice 100 in accordance with the present embodiment, the optical device100 having desired characteristics can be securely provided.

Also, in accordance with the present embodiment, when the optical filmthickness of the isolation layer 20 is an odd multiple of λ/4, the totaloptical film thickness of the first contact layer 111, thephotoabsorption layer 112 and the second contact layer 113 (i.e., thepin section) may preferably be an odd multiple of λ/4. FIG. 9 is a graphshowing the relation between the optical film thickness of the pinsection and the output of the optical device 100. In FIG. 9, currentsare plotted along the axis of abscissa, and outputs are plotted alongthe axis of ordinates. Also, FIG. 9 shows the relations with the opticalfilm thickness of the pin section being 13 times (an odd multiple) λ/4,13.5 times (between an odd multiple and an even multiple) λ/4, and 14times (an even multiple) λ/4, respectively.

As shown in FIG. 9, by setting the optical film thickness of the pinsection at an odd multiple of λ/4, the threshold current of the opticaldevice 100 can be reduced, compared to the cases of the other opticalfilm thicknesses.

On the other hand, in accordance with the present embodiment, asdescribed above, even when the optical film thickness of the pin sectionis set to an odd multiple of λ/4, the multilayer film obtained throughforming layers on the substrate 101 can be accurately evaluated.

In view of the above, by the method for manufacturing the optical device100 in accordance with the present embodiment, the optical device 100whose threshold value is reduced, and having desired characteristics canbe reliably provided.

4. Next, modified examples of the present embodiment are described. Itis noted that features different from those of the embodiment exampledescribed above (hereafter referred to as the “example of optical device100”) shall be described, and description of the other features shall beomitted. Also, members having similar functions as those of the exampleof optical device 100 shall be appended with the same reference numbers.

(1) First, a first modified example is described. FIG. 10 is a schematiccross-sectional view of an optical device 300 in accordance with themodified example.

In the optical device 300 in accordance with the modified example, adiode section 220 is formed on a support section 163 that is composed oflayers that are commonly formed with a first mirror 102, an active layer103 and a second mirror 104, respectively. It is noted that, as the topsurface of the support section 163 is at the same height as the topsurface of the second mirror 104, the diode section 220 can be said tobe formed on the second mirror 104.

The diode section 220 may be composed of a diode having a rectificationaction, such as, a pn junction diode, a Schottky barrier diode, or thelike. The diode section 220 may be electrically connected in parallelwith the surface-emitting laser section 140 by a first connectionelectrode 141 and a second connection electrode 142. The diode section220 may have a rectification action in a reverse direction with respectto that of the surface-emitting laser section 140.

The diode section 220 may include, as shown in FIG. 10, for example, afirst contact layer 211 formed on the support section 163, a capacitancereducing layer 212 formed on the first contact layer 211, and a secondcontact layer 213 formed on the capacitance reducing layer 212. Thefirst contact layer 211 may be composed of, for example, p-type GaAs,the capacitance reducing layer 212 may be composed of, for example, aGaAs layer in which no impurity is doped, and the second contact layer213 may be composed of, for example, n-type GaAs. In the presentmodified example, the entirety of the first contact layer 211, thecapacitance reducing layer 212 and the second contact layer 213corresponds to the semiconductor layer 122 of the example of opticaldevice 100. It is noted that the contact layer 311 that is formed on thesurface-emitting laser section 140 and is a layer common with the firstcontact layer 211 can electrically connect the second mirror 104 of thesurface-emitting laser section 140 with the second electrode 109.

In accordance with the present modified example, reflectance profilescan also be obtained by a first examination step and a secondexamination step, like the example of optical device 100, such that themultilayer film obtained through forming layers above the substrate 101can be accurately evaluated.

(2) Next, a second modified example is described.

In the present modified example, the substrate 101 in the example ofoptical device 100 may be separated by using, for example, an epitaxiallift off (ELO) method. In other words, the optical device 100 inaccordance with the present modified example may not be provided withthe substrate 101.

(3) Next, a third modified example is described. FIG. 11 is a diagramtypically showing the relation among an optical film thickness of asemiconductor layer 122, an optical film thickness of a sacrificiallayer 60, and the total optical film thickness of the semiconductorlayer 122 and the sacrificial layer 60 in accordance with the modifiedexample.

In the example of optical device 100, the case in which the optical filmthickness of the semiconductor layer 122 is an odd multiple or an evenmultiple of λ/4 is described. In the present modified example, theoptical film thickness of the semiconductor layer 122 is, for example,as shown in FIG. 11, greater than an odd multiple of λ/4, for example,greater than (λ/4)×(2m−1) (m is a natural number) and smaller than anintermediate value X between an odd multiple of λ/4 and an even multipleof λ/4, for example, smaller than (λ/4)×{2m−(½)}. The optical filmthickness of the sacrificial layer 60 is an odd multiple of λ/4, likethe example of optical device 100. Accordingly, the total optical filmthickness of the semiconductor layer 122 and the sacrificial layer 60 isgreater than an even multiple of λ/4, for example, greater than(λ/4)×2m, and smaller than an intermediate value Y between an evenmultiple of λ/4 and an odd multiple of λ/4, for example, smaller than(λ/4)×{2m+(½)}.

In accordance with the present modified example, reflectance profilescan also be obtained by a first examination step and a secondexamination step, like the example of optical device 100. Therefore, inthe case of the example described above, the reflection band W of thefirst mirror 102 and the second mirror 104 can be accurately observed inthe first examination step, and the Fabry-Perot wavelength λ_(f) can beaccurately measured in the second examination step.

It is noted that, in the present modified example, the relation betweenthe optical film thickness of the semiconductor layer 122 and the totaloptical film thickness of the semiconductor layer 122 and thesacrificial layer 60 is not limited to the example described above.Table 1 below shows, in a simplified fashion, combinations of theoptical film thickness of the semiconductor layer 122 and the totaloptical film thickness of the semiconductor layer 122 and thesacrificial layer 60, in the case of the example of optical device 100(a), and in the case of the modified example (b). Also, Table 1 showsitems (the reflection band W and the Fabry-Perot wavelength λ_(f))measured in the first examination step and the second examination step.

TABLE 1 Film Thickness of Film Thickness of Sacrificial First SecondSemiconductor Layer Layer Total Film Thickness Examination Examination(a) Odd Multiple Odd Even Multiple W λ_(f) Even Multiple Multiple OddMultiple λ_(f) W (b) Greater than Greater than W λ_(f) Odd Multiple EvenMultiple Smaller than Smaller than Intermediate Value X IntermediateValue Y Greater than Greater than λ_(f) W Intermediate Value XIntermediate Value Y Smaller than Even Smaller than Odd MultipleMultiple Greater than Even Greater than λ_(f) W Multiple Odd MultipleSmaller than Smaller than Intermediate Value Y Intermediate Value XGreater than Greater than W λ_(f) Intermediate Value Y IntermediateValue X Smaller than Odd Smaller than Even Multiple Multiple

(4) It is noted that the modified examples described above are onlyexamples, and the invention is not limited to these examples. Forexample, the modified examples may be appropriately combined.

5. Embodiments of the invention are described above in detail. However,a person having an ordinary skill in the art should readily understandthat many modifications can be made without departing in substance fromthe novel matter and effect of the invention. Accordingly, thosemodified examples are also deemed included in the scope of theinvention.

1. A method for manufacturing an optical device, the method comprisingthe steps of: forming a first multilayer film, including forming a firstmirror above a substrate, forming an active layer above the firstmirror, forming a second mirror above the active layer, forming asemiconductor layer on the second mirror, and forming a sacrificiallayer on the semiconductor layer; conducting a first examination step ofconducting a reflectance examination on the first multilayer film;forming a second multilayer film by removing the sacrificial layer fromthe first multilayer film; conducting a second examination step ofconducting a reflectance examination on the second multilayer film; andpatterning the second multilayer film to form a surface-emitting lasersection having the first mirror, the active layer and the second mirror,and a diode section having the semiconductor layer, the sacrificiallayer being formed to have an optical film thickness of an odd multipleof λ/4, where λ is a design wavelength of light emitted by thesurface-emitting laser section.
 2. A method for manufacturing an opticaldevice according to claim 1, the semiconductor layer being formed tohave an optical film thickness of an odd multiple or an even multiple ofλ/4.
 3. A method for manufacturing an optical device according to claim1, the semiconductor layer being formed to have an optical filmthickness of an odd multiple of λ/4, a reflection band of the firstmirror and the second mirror being measured in the first examinationstep, and a Fabry-Perot wavelength of light emitted by thesurface-emitting laser section being measured in the second examinationstep.
 4. A method for manufacturing an optical device according to claim1, the semiconductor layer being formed to have an optical filmthickness of an even multiple of λ/4, a Fabry-Perot wavelength of lightemitted by the surface-emitting laser section being measured in thefirst examination step, and a reflection band of the first mirror andthe second mirror being measured in the second examination step.
 5. Amethod for manufacturing an optical device according to claim 1, in thestep of removing the sacrificial layer, a layer among the semiconductorlayer in contact with the sacrificial layer functions as an etchingstopper layer.
 6. A method for manufacturing an optical device accordingto claim 5, the sacrificial layer being formed from InGaP, and the layeramong the semiconductor layer in contact with the sacrificial layerbeing formed from AlGaAs or GaAs.
 7. A method for manufacturing anoptical device according to claim 5, the sacrificial layer being formedfrom AlGaAs, and the layer among the semiconductor layer in contact withthe sacrificial layer being formed from GaAs.
 8. A method formanufacturing an optical device according to claim 1, the diode sectionbeing formed to be a photodetector section, and the semiconductor layerbeing formed to include a photoabsorption layer.
 9. A method formanufacturing an optical device according to claim 1, the semiconductorlayer including a first contact layer of a first conductivity type, anda second contact layer of a second conductivity type formed above thefirst contact layer.
 10. A method for manufacturing an optical deviceaccording to claim 1, each of the first mirror and the second mirrorbeing formed from a distributed Bragg reflection type mirror, and anoptical film thickness of each layer in the distributed Bragg reflectiontype mirror being λ/4.
 11. A method for manufacturing an optical devicecomprising: forming a first multilayer film, including forming a firstmirror above a substrate, forming an active layer above the firstmirror, forming a second mirror above the active layer, forming asemiconductor layer on the second mirror, and forming a sacrificiallayer on the semiconductor layer; conducting a first examination step ofconducting a reflectance examination on the first multilayer film;forming a second multilayer film by removing the sacrificial layer fromthe first multilayer film; conducting a second examination step ofconducting a reflectance examination on the second multilayer film; andpatterning the second multilayer film to form a surface-emitting lasersection having the first mirror, the active layer and the second mirror,and a diode section having the semiconductor layer, in the firstexamination step, one of a first measurement of measuring a reflectionband of the first mirror and the second mirror and a second measurementof measuring a Fabry-Perot wavelength of light emitted by thesurface-emitting laser section being conducted; and in the secondexamination step, the second measurement being conducted when the firstmeasurement is conducted in the first examination step, and the firstmeasurement being conducted when the second measurement is conducted inthe first examination step.
 12. An optical device wafer comprising: asubstrate; a first mirror formed above the substrate; an active layerformed above the first mirror; a second mirror formed above the activelayer; a semiconductor layer formed on the second mirror; and asacrificial layer formed on the semiconductor layer, the first mirror,the active layer and the second mirror being used to form at least aportion of a surface-emitting laser section, the semiconductor layerbeing used to form at least a portion of a diode section, and an opticalfilm thickness of the sacrificial layer being an odd multiple of λ/4,where λ is a design wavelength of light that is emitted by thesurface-emitting laser section.
 13. An optical device wafer according toclaim 12, an optical film thickness of the semiconductor layer being anodd multiple or an even multiple of λ/4.